[gmx-users] QMMM grompp error atom numbers fields.

Melchor S. meltxor.sanchez at hotmail.com
Tue May 24 16:57:17 CEST 2016

Dear members,

I am trying to run a QMMM simulation  in Gromacs4.5.5 using amber99sb-ILDN
together with orca. When I tried to run grompp I obtain the following error:

*  It appears as if you are trying to run a QM/MM calculation, but the
force  field you are using does not contain atom numbers fields. This is
an  optional field (introduced in Gromacs 3.3) for general runs, but
mandatory  for QM/MM. The good news is that it is easy to add - put the
atom number as  an integer just before the mass column in ffXXXnb.itp.  NB:
United atoms have the same atom numbers as normal ones.*

When I go through the forcefield itp file at
share/top/amber99sb-ildn.ff/ffnonbonded.itp I have seen that this
forcefield has an atom number column, or at least I have understood that it

[ atomtypes ]
; name      *at.num*  mass     charge ptype  sigma      epsilon
Br          *35*      79.90    0.0000  A   0.00000e+00  0.00000e+00
C           * 6 *     12.01    0.0000  A   3.39967e-01  3.59824e-01
CA           *6*      12.01    0.0000  A   3.39967e-01  3.59824e-01
CB       *    6 *     12.01    0.0000  A   3.39967e-01  3.59824e-01
CC           *6 *     12.01    0.0000  A   3.39967e-01  3.59824e-01

The 'at. num' column is the atom number? If it is, how can I solve this
error? Could you help me with that?

Thanks in advance,

Melchor Sanchez-Martinez

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